1. Field of the Invention
The present invention relates to an image forming apparatus which uses both of HDDs and an SSD, and which saves the power consumption.
2. Description of Related Art
In the international energy conservation program “International Energy Star Program”, an applicant is allowed to use the logo (mark) of the Program on a product which satisfies the specified energy conservation standard. The logo (in which the star mark and the term “ENERGY STAR” are drawn) can be used and indicated on the above product.
In the International Energy Star Program, at the time of the inauguration of the Program, in case of the energy conservation standard for a printer and a multi-function peripheral, only the standby energy is specified. Therefore, it was technically easy to satisfy the standard (obtain the qualification). However, in 2007, the standard was revised so as to judge the qualification by measuring the power consumption under the nearly actual use condition. As a result, the entire energy conservation including the energy conservation in the operating state of the printer is regained. In the new standard, the power consumption is measured by using the TEC (Typical Electricity Consumption) method for calculating the TEC value. Then, in the standard revised in 2013, by deciding the stricter standard, it is required to improve the performance relating to the energy conservation in both of the operating state and the standby state of the printer in order to satisfy the standard.
In an image forming apparatus, as a method for writing and reading the data at high speed, it is widely known that the RAID (Redundant Arrays of Inexpensive Disks) 0 (the RAID in level 0, hereinafter, referred to as “striping”) in which a plurality of HDDs (Hard Disk Drives) are activated in parallel and the data is dispersedly stored in the HDDs, is adopted. However, in the device having a large number of HDDs, a large amount of electricity is required.
The above problem can be solved by using one SDD (Solid State Drive) instead of a plurality of HDDs. The SDD is a storing device in which data can be written and read alone at high speed and in which the consumed power is lower as compared with the HDD.
However, the SDD has the upper limit on the number of times of rewriting data. Therefore, in case that only the SDD is used as the storing device, when the number of times of rewriting data reaches the upper limit, the data cannot be rewritten until the SDD is exchanged for a new one. As a result, the problem in which an image forming apparatus cannot be used, is caused. Further, in the SDD, the cost per unit capacity is high as compared with the HDD. Therefore, in consideration of the cost, the durability and the transfer speed of the storing device, it is preferable to use the SSD in combination with the HDDs.
For example, as the method for using the SDD in combination with the HDDs, in Japanese Patent Application Publication No. 2009-271637, the following method is disclosed. In the method, it is judged whether each storing device is the HDD or the SDD in the apparatus comprising a plurality of storing devices (HDDs and SDDs). The HDDs are activated in order (because a large amount of electricity is required at the spin-up in the HDDs). By activating the SDDs in parallel, the peak power consumption is suppressed.
In Japanese Patent Application Publication No. 2010-124076, the following method is disclosed. In the method, in the image processing apparatus comprising two storing devices which are different from each other in the time period necessary to enable the image to be read, the data to be read at the starting up of the apparatus is dispersedly stored in the above two storing devices. When the apparatus is started up, the data is read in order from the device in which the time period necessary to enable the image to be read is shorter. As a result, the time necessary to read the data at the starting up of the apparatus is shortened.
The method disclosed in Japanese Patent Application Publication No. 2010-124076, is the method for shortening the time necessary to read the data at the starting up of the apparatus. However, by the above method, the power consumption is not saved.
In the method disclosed in Japanese Patent Application Publication No. 2009-271537, it is possible to suppress the peak power consumption. However, by the above method, the power consumption which is caused in the operating state after the power supply is switched on is not saved.